The subject invention relates to a method for printing documents, and more particularly, to providing a method for determining the mechanism or printer on which the document was printed.
There are many different types of documents issued by government agencies, corporations and individuals that authorize the holder of such documents to perform authorized tasks or grant rights to the holder of such a document. Examples of such documents are drivers"" licenses, passports, entry access badges, identification cards, tickets, gift certificates, coupons, bonds, postal indicia, and the like.
With the advent of computers and refined printers that are available at a relatively low cost, the incidence of forgery of the above types of documents has proliferated. Although there are processes that apply coatings to documents to prevent copying, this does not end the problem of forgery.
Various schemes have been proposed to provide security to issued documents to inhibit forgeries of such documents. One such scheme is to use encryption so that a code can be derived that is based upon the information on the face of the issued document. Unfortunately, because of the limited space normally available in such documents, such a scheme often proves impractical.
The issuance of many types of tickets, such as theater tickets, is currently controlled by means of controlled supplies (e.g., serialized ticket stock, specially printed ticket stock, etc.) and by allowing tickets to be issued only by controlled, authorized issuers (e.g., ticket agents). Controlled supplies are expensive, difficult to control, and prone to theft or counterfeiting. Typically, one stood in line to purchase a ticket at the place the event was being held, or purchased the ticket over the phone from an authorized ticket agent who mailed the ticket to the purchaser.
Currently, ticketing companies are giving purchasers the option of printing their electronic tickets at home using ordinary paper, a personal computer printer, and an Internet connection. One of the problems in allowing people to print tickets at home is how to ensure that the tickets are not counterfeited. Furthermore, the printing technology used is another major factor, specifically when combined with the type of paper on which the ticket is printed.
Unfortunately, if a ticket is printed properly on ordinary paper with an encrypted bar code, the ticket can be photocopied, and the seller of the ticket will be unable to distinguish between the original ticket and the photocopied ticket.
This invention overcomes the disadvantages of the prior art by providing a method that determines whether or not a document was printed by a particular or specified printer. The invention provides a method that is able to determine the printer that produced a document in order to reduce the production of fraudulent documents. This invention utilizes the fact that printers render images that often contain unintended systematic errors that are a product of the design and manufacture of the printer. Even in the best printers, it is impossible to eliminate all possible sources of error. A printed image can be analyzed, and errors detected, thereby providing a xe2x80x98fingerprintxe2x80x99 that can be used to identify the printer (or product) used to print the image.
This invention provides a method for assigning unique printer resolutions or signatures, i.e., a unique number of dots per inch, to a class or models of printers or lines of postage meters. The number of dots per inch or resolution may be specified within an image on a document or within a postal indicia and later checked to determine if the image or document or the postal indicia has the correct resolution. The foregoing would be able to detect an image or postal indicia that was scanned into a computer and printed with a printer that did not have the number of dots per inch specified in the image or postal indicia.
In much the same way as described above, it is also possible to design xe2x80x98errorsxe2x80x99 or xe2x80x98defectsxe2x80x99 into the images appearing on documents, and the mechanism used to print an image, to be later used as a way of providing evidence that it was printed with a particular mechanism or printer. This invention makes use of these systematic xe2x80x98defectsxe2x80x99 to provide forensic evidence of where the image was printed. This invention also makes it difficult to reproduce the images exactly with commercially available printers. In so doing, the value of the image is increased, because it not only communicates information that is visible to the observer but it also contains a xe2x80x98fingerprintxe2x80x99 that identifies the source of the document and makes the document difficult to copy exactly.